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IRES-driven expression of the capsid protein of the Venezuelan equine encephalitis virus TC-83 vaccine strain increases its attenuation and safety.

Guerbois M, Volkova E, Forrester NL, Rossi SL, Frolov I, Weaver SC - PLoS Negl Trop Dis (2013)

Bottom Line: Here we describe a second generation of the recombinant TC-83 in which the subgenomic promoter is maintained and only the capsid protein gene is translated from the IRES.This VEEV/IRES/C vaccine candidate did not infect mosquitoes, was stable in its attenuation phenotype after serial murine passages, and was more attenuated in newborn mice but still as protective as TC-83 against VEEV challenge.Thus, by using the IRES to modulate TC-83 capsid protein expression, we generated a vaccine candidate that combines efficient immunogenicity and efficacy with lower virulence and a reduced potential for spread in nature.

View Article: PubMed Central - PubMed

Affiliation: Institute for Human Infections and Immunity, Sealy Center for Vaccine Development, and Department of Pathology, University of Texas Medical Branch, Galveston, Texas, United States of America.

ABSTRACT
The live-attenuated TC-83 strain is the only licensed veterinary vaccine available to protect equids against Venezuelan equine encephalitis virus (VEEV) and to protect humans indirectly by preventing equine amplification. However, TC-83 is reactogenic due to its reliance on only two attenuating point mutations and has infected mosquitoes following equine vaccination. To increase its stability and safety, a recombinant TC-83 was previously engineered by placing the expression of the viral structural proteins under the control of the Internal Ribosome Entry Site (IRES) of encephalomyocarditis virus (EMCV), which drives translation inefficiently in insect cells. However, this vaccine candidate was poorly immunogenic. Here we describe a second generation of the recombinant TC-83 in which the subgenomic promoter is maintained and only the capsid protein gene is translated from the IRES. This VEEV/IRES/C vaccine candidate did not infect mosquitoes, was stable in its attenuation phenotype after serial murine passages, and was more attenuated in newborn mice but still as protective as TC-83 against VEEV challenge. Thus, by using the IRES to modulate TC-83 capsid protein expression, we generated a vaccine candidate that combines efficient immunogenicity and efficacy with lower virulence and a reduced potential for spread in nature.

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Related in: MedlinePlus

Virulence in mice after injection of VEEV TC-83 and IRES-based viruses.Six-day-old CD1 mice received 5×104 PFU of indicated viruses SC, and were monitored 2 weeks for survival (A) and weight change (B). No deaths were recorded after day 14 post-infection.
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pntd-0002197-g006: Virulence in mice after injection of VEEV TC-83 and IRES-based viruses.Six-day-old CD1 mice received 5×104 PFU of indicated viruses SC, and were monitored 2 weeks for survival (A) and weight change (B). No deaths were recorded after day 14 post-infection.

Mentions: Because TC-83 does not typically induce mortality in adult mice, an infant mouse model was used to compare virulence of the vaccine constructs. Cohorts of 6-day-old CD-1 mice were inoculated subcutaneously with 5×104 PFU of TC-83, VEEV/mutSG/IRES/1 or VEEV/IRES/C and monitored for signs of illness, weight and survival. Another cohort of mice was inoculated with PBS as a negative control. As shown in Fig. 6A, while TC-83 induced 100% mortality by day 9 post-inoculation, the IRES-based viruses were both markedly attenuated (Logrank test, P<0.0001), with no significant difference observed between VEEV/mutSG/IRES/1 (76% survival) and VEEV/IRES/C (50% survival) at 14 days post-inoculation (P = 0.28). However, the mean weights recorded throughout the experiment indicated that growth of mice inoculated with VEEV/IRES/C was delayed compared to those inoculated with VEEV/mutSG/IRES/1 or PBS (P = 0.019 and P = 0.004 respectively, Fig. 6B), suggesting lesser attenuation of VEEV/IRES/C vaccine candidate compared to the previous IRES-based virus. However, the delayed growth in the VEEV/IRES/C was temporary and animals recovered in a few days, whereas no recovery was observed in the TC-83 group.


IRES-driven expression of the capsid protein of the Venezuelan equine encephalitis virus TC-83 vaccine strain increases its attenuation and safety.

Guerbois M, Volkova E, Forrester NL, Rossi SL, Frolov I, Weaver SC - PLoS Negl Trop Dis (2013)

Virulence in mice after injection of VEEV TC-83 and IRES-based viruses.Six-day-old CD1 mice received 5×104 PFU of indicated viruses SC, and were monitored 2 weeks for survival (A) and weight change (B). No deaths were recorded after day 14 post-infection.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3649961&req=5

pntd-0002197-g006: Virulence in mice after injection of VEEV TC-83 and IRES-based viruses.Six-day-old CD1 mice received 5×104 PFU of indicated viruses SC, and were monitored 2 weeks for survival (A) and weight change (B). No deaths were recorded after day 14 post-infection.
Mentions: Because TC-83 does not typically induce mortality in adult mice, an infant mouse model was used to compare virulence of the vaccine constructs. Cohorts of 6-day-old CD-1 mice were inoculated subcutaneously with 5×104 PFU of TC-83, VEEV/mutSG/IRES/1 or VEEV/IRES/C and monitored for signs of illness, weight and survival. Another cohort of mice was inoculated with PBS as a negative control. As shown in Fig. 6A, while TC-83 induced 100% mortality by day 9 post-inoculation, the IRES-based viruses were both markedly attenuated (Logrank test, P<0.0001), with no significant difference observed between VEEV/mutSG/IRES/1 (76% survival) and VEEV/IRES/C (50% survival) at 14 days post-inoculation (P = 0.28). However, the mean weights recorded throughout the experiment indicated that growth of mice inoculated with VEEV/IRES/C was delayed compared to those inoculated with VEEV/mutSG/IRES/1 or PBS (P = 0.019 and P = 0.004 respectively, Fig. 6B), suggesting lesser attenuation of VEEV/IRES/C vaccine candidate compared to the previous IRES-based virus. However, the delayed growth in the VEEV/IRES/C was temporary and animals recovered in a few days, whereas no recovery was observed in the TC-83 group.

Bottom Line: Here we describe a second generation of the recombinant TC-83 in which the subgenomic promoter is maintained and only the capsid protein gene is translated from the IRES.This VEEV/IRES/C vaccine candidate did not infect mosquitoes, was stable in its attenuation phenotype after serial murine passages, and was more attenuated in newborn mice but still as protective as TC-83 against VEEV challenge.Thus, by using the IRES to modulate TC-83 capsid protein expression, we generated a vaccine candidate that combines efficient immunogenicity and efficacy with lower virulence and a reduced potential for spread in nature.

View Article: PubMed Central - PubMed

Affiliation: Institute for Human Infections and Immunity, Sealy Center for Vaccine Development, and Department of Pathology, University of Texas Medical Branch, Galveston, Texas, United States of America.

ABSTRACT
The live-attenuated TC-83 strain is the only licensed veterinary vaccine available to protect equids against Venezuelan equine encephalitis virus (VEEV) and to protect humans indirectly by preventing equine amplification. However, TC-83 is reactogenic due to its reliance on only two attenuating point mutations and has infected mosquitoes following equine vaccination. To increase its stability and safety, a recombinant TC-83 was previously engineered by placing the expression of the viral structural proteins under the control of the Internal Ribosome Entry Site (IRES) of encephalomyocarditis virus (EMCV), which drives translation inefficiently in insect cells. However, this vaccine candidate was poorly immunogenic. Here we describe a second generation of the recombinant TC-83 in which the subgenomic promoter is maintained and only the capsid protein gene is translated from the IRES. This VEEV/IRES/C vaccine candidate did not infect mosquitoes, was stable in its attenuation phenotype after serial murine passages, and was more attenuated in newborn mice but still as protective as TC-83 against VEEV challenge. Thus, by using the IRES to modulate TC-83 capsid protein expression, we generated a vaccine candidate that combines efficient immunogenicity and efficacy with lower virulence and a reduced potential for spread in nature.

Show MeSH
Related in: MedlinePlus